1. Field of the Invention
This invention relates to a slide fastener having die-cast coupling elements treated by an electrochemical surface treatment such as electrolyte plating or electrodeposition painting.
2. Description of the Related Art
In the manufacture of slide fasteners, it is currently known to treat a plurality of metal coupling elements with electrochemical surface treatment such as electrotytic plating or electrodeposition painting, after the coupling elements are mounted on a pair of stringer tapes at regular distances along their confronting inner longitudinal edges. In this case, the electrochemical surface treatment is done while an electric current is conducted to the individual coupling elements; for this purpose, a conductive wire is incorporated in the inner longitudinal tape edge on which the successive coupling elements are mounted.
This prior art is exemplified by Japanese Utility Model Publications Nos. SHO 39-8208 and SHO 59-7136 and U.S. Pat. No. 2,264,324 (Cl. 204-23), in which the conductive wire is situated alongside a core thread extending along the inner longitudinal tape edge or is wound around such a core thread. According to these prior art publications, the conductive wire is attached to the outside edge of the core thread, projecting from the peripheral surface of the core thread.
In the case where the metallic coupling elements are die-cast, the stringer tape is held between upper and lower mold halves, and then molten metal is introduced into the mold to form a plurality of coupling elements on the stringer tape at equal distances along the inner longitudinal edge. The upper and lower mold halves have grooves extending between the individual cavities for forming the coupling elements; the grooves serves to receive the inner longitudinal edge of the stringer tape during die-casting. The contour of the grooves must be such that the conductive wire bites into the core thread so as not to project from the grooves. With the conductive wire projecting from the grooves, the upper and lower mold halves cannot be brought into intimate contact with each other. In the foregoing prior art, however, the projected portion of the conductive wire would be caught between the groove edges of the upper and lower mold halves and hence would possibly be cut off so that electrolytic plating will be impossible. Since the conductive wire is exposed along the entire length of the core thread, thus impairing the appearance of the slide fastener as a finished product.